Interpretive Summary: Giardiasis is an intestinal parasitic disease in humans and animals caused by the protozoan Giardia lamblia. Although there are drugs available to treat giardiasis, these drugs often have undesirable side effects. One possible way to prevent or treat giardiasis infection is to administer antibodies that react with G. lamblia, and thereby prevent the parasite from attaching to cells lining the gut. In the present study, a gene coding for a protein that is a part of the parasite involved in attachment, namely the ventral disk, was cloned using molecular techniques, and then inserted into Escherichia coli to produce the recombinant form of the protein. Antibodies were made to the recombinant protein, called delta giardin, and were used to identify the parasite protein on the ventral disk. An interesting observation was that treating G. lamblia with antibodies to delta giardin could prevent the parasite from attaching to substrate in cell culture. These findings should be of interest to the medical community since they suggest that anti-delta giardin antibodies could be useful in preventing or treating giardiasis.

Technical Abstract:
A cDNA coding for d-giardin was cloned from Giardia lamblia trophozoites in order to localize the protein and study its function in mediating surface attachment. Recombinant d-giardin antigen was produced in Escherichia coli as a poly-histidine fusion protein and was purified by affinity chromatography for production antisera to d-giardin. By immunoblotting analysis, antisera to recombinant d-giardin antigen recognized a 31 kDa protein in G. lamblia trophozoites. Anti-recombinant d-giardin was used to localize the native protein to the trophozoite ventral disk in both immunofluorescence and immunoelectron microscopy assays. Pre-treatment of G. lamblia trophozoites with anti-d-giardin sera caused morphological changes in the parasite, and inhibited trophozoite binding to cell culture surfaces. Binding of antibodies to d-giardin may provide a means of inhibiting attachment of G. lamblia trophozoites to the intestinal epithelium, and thereby prevent clinical giardiasis.